One of the things I questioned when I really started to think about trans stuff is why does 'gender' have to 'match' biological sex? What does it even MEAN for gender to 'match' sex? It is that if you are female you must behave and think in a feminine way, and if you are male you must behave and think in a masculine way (depending on the social construct of masculine and feminine?)
What's shocked me is the amount of people for whom 'female', as in actual sex, and 'feminine', as in cultural/social attributes, are so closely intertwined and conflated they are literally unable to see them as different things. To them, being physically female means in all cases being feminine, and being feminine means in all cases being physically female. They use the words interchangeably and really need it spelling out that they mean quite different things.